Your body has a huge store of body fat to fuel exercise. There’s no need to down dietary fat. Exercise needs carbs for energy.

I mean, the first sentence negates the second one because it suggests that carbs are not needed for energy (as fat already provides for energy), which I'd largely agree with.

In fact, the latest research that has gone through more than 160 studies suggests that exogenous carbs don't need to go beyond ~10 grams per hour to maximize performance, which is like 1 fig:

My take on that quote is that carb loading prior to exercise is not useful. And for the most part I have always thought that carb loading is bunk.

And as for that 10 g/h during the exercise is beneficial compared to no carbohydrate. That was when comparing those on a low carb daily intake with others on a higher carb daily intake. That group saw no difference during submaximal prolonged exercise. But persons from either group getting benefit when using the 10 g/h during that exercise.

They don't quite get into the difference when more is used. Which I expect is a diminishing return. And at some point detrimental.

I personally didn't find anything novel about this study that impacts my overall thinking and action on when I use carbohydrate.

Although I will say that taking a small nibble out of one dried fig 4 to 6 times during a high effort ride is going to be difficult. I'd rather just put the carbohydrate in my bottle so I get both hydration and carbohydrate at the same time.

While you can "survive" while exercising at a low intensity without taking in carbs, athletes performing at moderate or greater intensities benefit greatly from carb ingestion. There are much data to confirm this, going back decades.

Also, 10 g/hr is well below the ACSM guideline of 30-60 g/hr for endurance exercise greater than 1 hour.

Many if not all of those studies, spanning over 100 years of literature, are covered in the above paper, and there are many other interesting bits, like the observation that ingesting carbs will lead to more glycogen depletion, which seems paradoxical.

By the way, I don't care to convince you or anybody else on this topic, nor to suggest that one is required to not do over X amount of carbs per hour, only that it is not necessary to do so, which are two very different things, but the article makes for an interesting read nonetheless.

There seems to be a consensus among researchers that aerobic exercise performed in zones 1 and 2 (using the 5-zone scale) burns fat almost exclusively, whereas exercise in zone 3 and above burns carbs at a rate that increases as the effort increases.

This explains it perfectly on the White Board.

Here is the proof of that, at least for me, now.
I had a VO2Max test where is cycled with a breathing tube analyzing my breath at increasing load. What I see confirms, that around 140-145 I switch from burning mostly fat to carbs. That resistance value, which I assume is watts, is my Zwift measured FTP. At max HR of 163, no fat, all carbs and probably a few brain cells too.

Yes, here's a rough example graph of carbs and fat usage (grams/minute) by intensity:




Zone 2 is already gobbling up the carbs. It's worthwhile to know that you can still deplete your glucose in zone 2, so even zone 2 efforts of 90 minutes or more benefit from carb ingestion, mainly by reducing fatigue from declining blood glucose.

Wearing a continuous glucose monitor (CGM) seems to be all the rage, and from what I understand, against racing rules.
I am wondering if anyone here, or any has read about measuring like this during a ride, for a nondiabetic person. When we hit the dreaded bonk, I wonder what the blood glucose level might be. Anyone know?

Did you all know that when you exercise the body doesn't need insulin to shuttle gluclose....

https://diabetes.org/health-wellness...se-blood-sugar

BTW, if one does "bonk" you can expect the glucose numbers to be fairly low; however, you can also expect a sharp rise in glucose levels during intense exercise. I know this from experience, because I got a blood test directly after a hard ride and my level was about 110 -- and many other readings were off the chart, which was after fasting for over 12 hours. I retook the test a couple days after and all was normal.




.

Shouldn't the blood glucose levels come within normal range again after a few couple of hours max?

Perhaps this explains getting a "second wind?"

I do know that we have a tremendous store of energy in fat, muscles etc., but I do not know the speed at which that all happens. Nor how fast food carbs are absorbed, or else you could keep eating and ride forever.

Well, yes of course we can. PBP attracts a lot of riders. I've ridden with a few finishers. They're not abnormal, they just know how to keep going, which of course means keep eating. I've only done 400k rides, but 18 hours ET is a long time. I'd usually be stronger at the end than at the beginning, as then I'd know when the end was. I'd eat mostly carbs, a little protein, very little fat. I'd have a couple slices of pizza at the end, drive home and go to bed.

Way early in my bike life, like when I was maybe 53 and rode my first 50 mile ride. After about 30 miles, I started to feel dizzy, got off the bike and sat in the ditch while the world went around. I ate a bagel, drank some water, and 10 minutes later was on my way again. Never did that again. One has to keep up a steady intake. I start eating after the first 15' and then eat every 15', establishing a pattern. No need to wait until one is sitting in a ditch.

That said, as the years went by, I became more resilient but on serious really long rides would still eat every 15'.

Not true... school lunch programs, food served to armed forces.. SNAP program foods.. food in government hospitals.. etc.. etc... etc are mandated to follow these guidelines... the guidelines matter directly... daily... for 10s of millions of Americans... for good or bad! 😳

This is of course for carb adapated athletes.. fat adapted atheletes have been show to metabolize fat at a rate of as hight as 1.6g/min at 86% VO2max.. fat adapated atheles have shown fat metabolism as high at 1.8g/min in another study!

"Low carbohydrate high fat ketogenic diets on the exercise crossover point and glucose homeostasis"
Journal Frontiers in Physiology in 2023.
https://www.frontiersin.org/journals...3.1150265/full

No, it's for trained endurance athletes who can be considered both "fat adapted" and "carb adapted".

Considered more efficient at burning fat would be a better description. Being dual fuel is spectrum - some better at burning fat, some not.

-Some fat adaptation, meaning better than the couch potato, happens in active people/endurance based people.

-More fat adaptation occurs when athletes train in carb depleted states.

-True fat adaptation doesn't really occur for 2-3-4++ months of being in complete ketosis.

We need to see a chart like the one you posted where the subjects are truly fat adapted athletes. I'm not talking using subjects that are two weeks into ketosis - which many of the studies out there are based on - I'm talkin long term, well trained "keto" type athletes.

I suspect there would be a shift in the fuel changeover points.

I know for me personally - 6+ years fat adapted, but not an athlete - I can go into mid Z3/tempo range for 2+ hours on a day where I didn't consume any extra carbs and only consume about 20+/- per hour to keep the blood glucose topped off. Blood glucose and muscle glucose are two different systems - if BG's dip, you can feel like you are bonking - but still have plenty in the muscle "tank".

Again, personally - I don't "blow up" until I hit prolonged bouts of sweet spot or above. Or if I push into Z4/Z5 too often on longer efforts, like a century.

Just for clarity - I am not saying that fat is a superior energy source for bike racers. It's not.

double...

The old food pyramid existed when I was a kid, and obesity was rare. Breakfast was always a huge bowl of cereal which had the word "sugar" in the name, and I could always pour in a little more if my "Super Sugar Crisps" or "Sugar Smacks," or "Sugar Frosted Flakes" weren't sweet enough. Lunch was PB&J (with extra J) on Wonder Bread, and half pint (or 2) of chocolate milk. Dinner was meat; burgers, pork chops, round steak, meat loaf, or chicken, with some sort of vegetable, and bread. I pretty much never drank water, except from the fountain at school during PE. Breakfast and lunch were chocolate milk, Koolaid or soft drinks later in the day, milk at dinner. I ate as much candy as my allowance and grass cutting could pay for. Candy bars were 25 cents each (formerly 20 cents each, but inflation sucked in those days), and I'd eat them (all 4 of them) on the way home from the store.

But kids were physically active. We had PE every day at school, every kid played some kind of sport, for me it was little league. Or I'd hop on my BMX bike and ride out to the river (10 mile round trip) to break/burn/blow something up, or terrorize wild animals with my wrist rocket sling shot (I was a bad kid). We had ball games on the street in front of our homes from after homework until dinner time. In the warmer months we could swim at the community pool, or take the bus to the beach for 45 cents. No video games, no computers, no phones, very little TV except on Saturday mornings and 7pm to 9pm on weekdays.

Kids -

All of my kids are/were active in sports all year round. My girls swam year round with groups of other girls that swam year round. Two a day practices, team USA swimming, and down in SC - neighborhood swim teams were locally super competitive. Very few of these kids were skinny like the old days.

My son currently races MTB's - there are a bunch of soft bodies in his league, same when he wrestled.

I also pay attention when I visit my daughters at college, even noticed this a bit when they were in HS: (this may go over like a led balloon)
-Both boy and girl body types have changed. Not just becoming soft bodied, but less differentiation between the two.

I work with a young Chem E - brilliant kid. Masters degree, MBA, PE - working on a PHD. When he first came to work with us fresh out of college - my office picked up a few jobs to expand food processing plants. We learned the ingredients and additives being put in these foods - and he has the understanding of what they do to the human body.

He personally struggles with a soft body - in his own words, there is no man in him - even after years of MMA style training.... and he is the reason I pay attention at my kids schools. He flat said our body types are being shifted by the additives/hormones and chemicals in our processed foods. Male and female hormones are muted - creating blended body types with little difference. And our brief work in the industry backed his claims.

All we need to do is look at our youth. Soft, heavy, high levels of metabolic disease, lack of hormone production...

”Third, endurance athletes exercising at >85%VO2max, whilst performing 6 × 800 m running intervals, measured the highest rates of fat oxidation yet reported in humans. Peak fat oxidation rates measured at 86.4 ± 6.2%VO2max were 1.58 ± 0.33 g/min with 30% of subjects achieving >1.85 g/min.”

well, I guess you can call them whenever you want… BUT… athletes that had been on ketogenic diet for a month have been showing to have a crossover point at 85% of VO2 max and fat anabolism rate of 1.6 g per minute.

I sent you a link to an actual study that demonstrates that and I could send more similar ones… Where does the information come from, for your chart? Do you know how they we eating off the bike. Clearly, from link I posted, what you eat off the bike has a pronounced and significant affect on fat metabolism on the bike!

Low carbohydrate high fat ketogenic diets on the exercise crossover point and glucose homeostasis

https://pubmed.ncbi.nlm.nih.gov/37057184/#:~:text=Third%2C%20endurance%20athletes%20exercising%20at,achieving%20%3E1.85%20g%2Fmin.

And you’ve done a study demonstrating that?.. Read the study I’ve linked to.. this is simply not true.

Athletes that don’t adopt to a ketogenic diet for at least a month have your chat.. those that do can metabolize fat at a way higher rate and have way higher crossover points… this is proven at this point at. You can BELIEVE whatever you want, but at some point you should deal with proven fact.. no?

Q: can a person actually become "adapted" or is this simply physiology?
Q2: Would not an athlete who is termed "adapted" also be a fitter person, thus being stronger, faster, etc.?
Q3: Bonus question. If I am both fat and carb "adapted" before that was what, protein adapted? That is all that is left.

OK, one more. According to my recent VO2 Max test, I switch from burning fat to carbs around 85% of my max HR. So, right around there is where I should train, right? According to the analysis that I was given, that is Zone 2, but in all honest, that is too high for me to sustain over a long period.

Edit: that Z2 was from my actual test. RWGPS calculates that as a Zone 4 HR, which fits better with my perceived rate of exertion or whatever that is called.